The effect of sugar removal on the structure of the Fc region of an IgG antibody as observed with single molecule Förster Resonance Energy Transfer

• Single molecule FRET can be used to study the structure of the Fc region of IgG.
• FRET results for glycosylated IgG agree with crystal structure results.
• FRET results for deglycosylated IgG indicate a wide range of Fc conformations.
• Deglycosylation appears to enhance the flexibility of the Fc region of IgG.

The deglycosylation of immunoglobulin G (IgG) antibodies leads to a diminished immune response. This reduction in immune response is thought to arise from weakened binding of IgG antibodies to effector molecules as a result of a conformational change in the antibody. The nature of this structural alteration is uncertain due to the conflicting results obtained from different experimental methods. We have examined the impact of deglycosylation by the endoglycosidase PNGase F on the structure of the Fc region of a human IgG antibody using single molecule Förster Resonance Energy Transfer (FRET). The FRET efficiency histograms obtained indicate that the structure of the Fc region becomes more flexible upon deglycosylation. This is demonstrated by a change in the width of the energy transfer efficiency peak, which increases from 0.19 ± 0.02 to 0.6 ± 0.1 upon deglycosylation.